In the more sophisticated switch device, there are more types of protocol messages to process, if these messages are all processed by CPU, CPUs with stronger processing ability need to be selected. However, this will increase the cost inevitably, and also decrease the competitiveness of products; further, with regard to some protocol messages which are sensitive to time, the requirements are difficult to meet even though the CPU with stronger processing ability are chosen. Generally, in this case, an extended processor chip is needed to be externally attached to the switch chip to assist to accomplish certain processing for protocol message.
A physical port connected to CPU in a switch chip is generally special port of the switch chip, when CPU is receiving packets, the message would carry source physical port information; the CPU may designate destination port when sending the packet, so that CPU could receive and send packet normally. However, if the port which connects the switch chip and the extended CPU is normal physical port, the switch chip cannot make the message carry source physical port information when the extended processor is receiving the packets; the switch chip cannot designate the destination physical port of the message when the extended processor is sending the packets, which would lead to that the action of transmitting message between the extended processor and the switch chip cannot be carried out.